Added StringPiece overloads for base::JoinString.

base/strings/string_util.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
 // This file defines utility functions for working with strings.
 
 #ifndef BASE_STRINGS_STRING_UTIL_H_
 #define BASE_STRINGS_STRING_UTIL_H_
 
 #include <ctype.h>
@@ skipping 411 matching lines @@
 // immediately write over this memory, but there is no other way to set the size
 // of the string, and not doing that will mean people who access |str| rather
 // than str.c_str() will get back a string of whatever size |str| had on entry
 // to this function (probably 0).
 BASE_EXPORT char* WriteInto(std::string* str, size_t length_with_null);
 BASE_EXPORT char16* WriteInto(string16* str, size_t length_with_null);
 #ifndef OS_WIN
 BASE_EXPORT wchar_t* WriteInto(std::wstring* str, size_t length_with_null);
 #endif
 
 // Does the opposite of SplitString().

[danakj, 2017/02/16 16:34:32]

and SplitStringPiece()

[Matt Giuca, 2017/02/17 06:09:59]

Done.

 BASE_EXPORT std::string JoinString(const std::vector<std::string>& parts,
                                    StringPiece separator);
 BASE_EXPORT string16 JoinString(const std::vector<string16>& parts,
                                 StringPiece16 separator);
+BASE_EXPORT std::string JoinStringPiece(const std::vector<StringPiece>& parts,
+                                        StringPiece separator);
+BASE_EXPORT string16 JoinStringPiece(const std::vector<StringPiece16>& parts,
+                                     StringPiece16 separator);
 
 // Replace $1-$2-$3..$9 in the format string with values from |subst|.
 // Additionally, any number of consecutive '$' characters is replaced by that
 // number less one. Eg $$->$, $$$->$$, etc. The offsets parameter here can be
 // NULL. This only allows you to use up to nine replacements.
 BASE_EXPORT string16 ReplaceStringPlaceholders(
     const string16& format_string,
     const std::vector<string16>& subst,
     std::vector<size_t>* offsets);
 
@@ skipping 11 matching lines @@
 
 #if defined(OS_WIN)
 #include "base/strings/string_util_win.h"
 #elif defined(OS_POSIX)
 #include "base/strings/string_util_posix.h"
 #else
 #error Define string operations appropriately for your platform
 #endif
 
 #endif  // BASE_STRINGS_STRING_UTIL_H_